U.S. patent application number 10/127613 was filed with the patent office on 2002-10-31 for semiconductor device and method for manufacturing semiconductor device.
Invention is credited to Teshima, Takanori.
Application Number | 20020158333 10/127613 |
Document ID | / |
Family ID | 18976372 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020158333 |
Kind Code |
A1 |
Teshima, Takanori |
October 31, 2002 |
Semiconductor device and method for manufacturing semiconductor
device
Abstract
A semiconductor device includes a semiconductor chip generating
heat, a pair of heat sinks, which face each other, to conduct heat
from both surfaces of the chip, a pair of compressible insulating
sheets, and a mold resin covering the chip, the heat sinks, and the
sheets such that the sheets are exposed from the surface of the
resin. The mold resin is prevented from covering the outer surfaces
of the heat sinks, which are pressed by mold parts, and breakage of
the chip is avoided during molding. The plates are insulated by the
sheets, so no dedicated insulating sheets for the heat sinks are
needed after the device is completed.
Inventors: |
Teshima, Takanori;
(Okazaki-city, JP) |
Correspondence
Address: |
LAW OFFICES OF DAVID G. POSZ
2000 L STREET, N.W.
SUITE 200
WASHINGTON
DC
20036
US
|
Family ID: |
18976372 |
Appl. No.: |
10/127613 |
Filed: |
April 23, 2002 |
Current U.S.
Class: |
257/718 ;
257/706; 257/719; 257/E21.504; 257/E23.092; 257/E23.126; 438/122;
438/125 |
Current CPC
Class: |
H01L 2924/14 20130101;
H01L 2924/01013 20130101; H01L 2224/48247 20130101; H01L 24/45
20130101; H01L 2224/73215 20130101; H01L 21/565 20130101; H01L
2924/181 20130101; H01L 2924/01082 20130101; H01L 24/32 20130101;
H01L 2224/45124 20130101; H01L 2224/73265 20130101; H01L 23/4334
20130101; H01L 2924/1301 20130101; H01L 2224/83951 20130101; H01L
2924/01079 20130101; H01L 2924/13055 20130101; H01L 2924/01033
20130101; H01L 24/33 20130101; H01L 2924/01014 20130101; H01L
2224/2612 20130101; H01L 2224/48091 20130101; H01L 24/48 20130101;
H01L 2224/8592 20130101; H01L 23/3135 20130101; H01L 2224/32245
20130101; H01L 2924/01029 20130101; H01L 2924/1305 20130101; H01L
2924/01006 20130101; H01L 2224/45144 20130101; H01L 2924/01005
20130101; H01L 2224/45124 20130101; H01L 2924/00014 20130101; H01L
2224/45144 20130101; H01L 2924/00014 20130101; H01L 2224/48091
20130101; H01L 2924/00014 20130101; H01L 2224/73265 20130101; H01L
2224/32245 20130101; H01L 2224/48247 20130101; H01L 2924/1301
20130101; H01L 2924/00 20130101; H01L 2924/1305 20130101; H01L
2924/00 20130101; H01L 2924/181 20130101; H01L 2924/00012
20130101 |
Class at
Publication: |
257/718 ;
257/706; 438/122; 438/125; 257/719 |
International
Class: |
H01L 023/10; H01L
023/34; H01L 021/44; H01L 021/48 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 25, 2001 |
JP |
2001-127516 |
Claims
1. A semiconductor device comprising: a semiconductor chip, which
produces heat when operated; a pair of heat conducting plates for
conducting heat from opposite surfaces of the chip, wherein the
plates face each other; a pair of insulating sheets, which are
compressively deformable, adhered to the heat conducting plates;
and a resin molding covering the chip, the plates, and the sheets
such that the sheets are exposed from the resin molding.
2. The semiconductor device of claim 1, wherein the heat
conductivity of the insulating sheets is greater than that of the
resin molding.
3. The semiconductor device of claim 2, wherein the insulating
sheets are made of silicone rubber.
4. The semiconductor device of claim 1, wherein the material of one
of the insulating sheets is different from the material of the
other insulating sheet.
5. The semiconductor device of claim 1, wherein the thickness of
one of the insulating sheets is different from the thickness of the
other insulating sheet.
6. The semiconductor device of claim 1, wherein the surface
characteristics of one of the insulating sheets is different from
the surface characteristics of the other insulating sheet.
7. The semiconductor device of claim 1, wherein the insulating
sheets are adhered to the heat sinks using a coating resin applied
to the surfaces of the heat sinks.
8. The semiconductor device of claim 7, wherein the coating resin
is polyamide resin.
9. The semiconductor device of claim 1, wherein the chip forms part
of a stack, and the stack includes the plates, and opposite sides
of the chip are soldered to members of the stack.
10. A method for manufacturing a semiconductor device that includes
a semiconductor chip comprising: locating the chip between two heat
conducting plates; attaching an insulating sheet to an outer
surface of each of the plates; filling a space around the chip and
the plates and between the sheets with resin by molding.
11. The method of claim 10 further comprising applying a resin
coating material on the chip and the plates after locating the chip
between the plates.
12. The method of claim 11, wherein the sheets are adhered to the
plates with the resin coating material.
13. The method of claim 11, wherein the resin coating material is
applied by immersing the chip and the plates in a container of
liquid that includes the resin coating material.
14. The method of claim 11, wherein the resin coating material is
applied by dripping or spraying a liquid that includes the resin
coating material on the chip and the plates.
15. The method of claim 11, wherein the resin coating material is
polyamide resin.
16. A method for manufacturing a semiconductor device that includes
a semiconductor chip comprising: soldering opposite sides of the
chip to members of a stack, which includes two heat conducting
plates, such that the chip is located between the plates; attaching
a compressible insulating sheet to an outer surface of each of the
plates; filling a space around the chip and the plates and between
the sheets with resin by molding.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on and incorporates herein by
reference Japanese Patent Application No. 2001-127516, which was
filed on Apr. 25, 2001.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a semiconductor device in
which a semiconductor chip generating heat is located between a
pair of heat sinks and to a method for manufacturing the
device.
[0003] A semiconductor chip such as a power IC, which controls a
large amount of electric power and current, generates so much heat
that a semiconductor device using the chip requires a heat sink to
dissipate heat. As shown in FIG. 4, in a proposed semiconductor
device 1, a semiconductor chip 4 and a heat sink coupler 5 are
located between a pair of heat sinks 2, 3. One heat sink 2 and the
chip 4 are soldered together, the chip 4 and the coupler 5 are
soldered together, and the coupler 5 and the other heat sink 3 are
soldered together. A mold resin 7 covers the chip 4, the heat sink
coupler 5, and the heat sinks 2, 3 such that the heat sinks 2, 3
are exposed from the surface of the resin 7. Because the resin 7
covers neither of the outer surfaces of the heat sinks 2, 3, heat
is efficiently transferred from the heat sinks 2, 3 from both sides
of the chip 4.
[0004] The semiconductor device 1 is molded in a mold 8 that
includes a lower mold 8a, an upper mold 8b, and a movable mold 8c,
as shown FIG. 4. The movable mold 8c presses the device 1 during
the molding to prevent the resin 7 from covering the outer surfaces
of the heat sinks 2, 3 while adjusting the pressure applied to the
device 1 during molding. Therefore, the structure of the mold 8 is
relatively complicated and the production cost of the mold 8 is
relatively high. Thus, the production cost of the semiconductor
device 1 is relatively high. Although the pressure applied to the
device 1 is controlled, the semiconductor chip 4 tends to break
during the molding because there is nothing to limit the force the
chip 4 receives from the mold 8.
[0005] In addition, the outer surfaces of the heat sinks 2, 3 need
to be insulated when the completed device 1 is inspected, screened,
or assembled into a unit such as an inverter unit. For example, as
shown in FIG. 5, when the device 1 is located between a pair of
cooling plates 9, two heat conducting sheets 10 made of insulating
material are inserted between the plates 9 and the outer surfaces
of the heat sinks 2, 3.
[0006] Moreover, a coating resin such as polyamide resin is applied
to the surface of the heat sinks 2, 3 prior to the molding to
create a desired adhesion between the heat sinks 2, 3 and the mold
resin 7. However, in the semiconductor device 1, the distance
between the heat sinks 2, 3 is in the range between 1 and 2 mm, so
it is difficult to apply the coating resin on the inner surfaces of
the heat sinks 2, 3. It is also difficult to inspect the coating
quality.
SUMMARY OF THE INVENTION
[0007] The present invention has been made in view of the above
problems with an object to provide a semiconductor device that
makes it possible to use a mold having a simple structure without
damaging a semiconductor chip during molding, makes it unnecessary
to insulate both outer surfaces of the heat sinks using dedicated
insulating sheets after the device is completed, and makes it
easier to apply coating resin on a pair of heat sinks in the
manufacturing process of the device.
[0008] Insulating sheets, which are made of compressively
deformable material, are adhered to the outer surfaces of the heat
sinks, and the device is molded in a mold while the sheets are
located between the mold and the heat sinks. The sheets are
compressively deformed during the molding to prevent the chip from
being broken, even if an economical mold having a simple structure
is used. The plates are insulated by the sheets to make dedicated
insulating sheets unnecessary when the completed device is
inspected, screened, or assembled into a unit such as an inverter
unit. The coating resin is coated by immersing the chip and the
heat sinks in a solution containing the resin to simplify the
coating.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The above and other objects, features and advantages of the
present invention will become more apparent from the following
detailed description made with reference to the accompanying
drawings. In the drawings:
[0010] FIG. 1 is a cross-sectional view of a semiconductor device
in a mold according to the present invention;
[0011] FIG. 2A is a diagrammatic exploded perspective view showing
a process stage of a method for making the semiconductor device of
FIG. 1;
[0012] FIG. 2B is a diagrammatic perspective view showing a process
stage of a method for making the semiconductor device of FIG.
1;
[0013] FIG. 2C is a diagrammatic perspective view showing a process
stage of a method for making the semiconductor device of FIG.
1;
[0014] FIG. 2D is a diagrammatic exploded perspective view showing
a process stage of a method for making the semiconductor device of
FIG. 1;
[0015] FIG. 2E is a diagrammatic cross sectional view showing a
further process stage of a method for making the semiconductor
device of the invention;
[0016] FIG. 3 is a cross-sectional view of a semiconductor device
located between a pair of heat-transfer members;
[0017] FIG. 4 is a cross-sectional view of a proposed semiconductor
device; and
[0018] FIG. 5 is an exploded cross-sectional view of the proposed
semiconductor device located between a pair of heat-transfer
plates.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] As shown in FIG. 1, a semiconductor device 11 includes a
semiconductor chip 12, which generates heat, a lower heat sink 13
and an upper heat sink 14, which conduct the heat generated by the
semiconductor chip, and a heat sink coupler 15. The lower surface
of the chip 12 and the upper surface of the lower heat sink 13 are
connected by solder 16, the upper surface of the chip 12 and the
lower surface of the heat sink coupler 15 are soldered together,
and the upper surface of the heat sink coupler 15 and the lower
surface of the upper heat sink 14 are soldered together. The heat
generated by the chip 12 is conducted through the heat sinks 13 and
14.
[0020] In this embodiment, the semiconductor chip 12 is a power
semiconductor such as an IGBT (Insulated Gate Bipolar Transistor)
and a thyristor in the shape of a thin rectangular plate, as shown
in FIG. 2A. The lower heat sink 13, the upper heat sink 14, and the
heat sink coupler 15 are made of metal having high heat
conductivity and electric conductivity, such as copper or aluminum.
The lower heat sink 13 and the upper heat sink 14 are connected
electrically to a pair of electrodes such as collector and emitter
electrodes by the solder 16.
[0021] The lower heat sink 13 is a rectangular plate and is
integrated with a terminal 13a which is a rectangular plate
extending rearward in FIG. 2A. The heat sink coupler 15 is a
rectangular plate and is a little smaller in area than the
semiconductor chip 12. The upper heat sink 14 is a rectangular
plate and is integrated with another terminal 14a, which is a
rectangular plate extending rearward in FIG. 2D. The terminals 13a,
14a do not face one another; that is, they are offset from one
another as shown in FIG. 2D. The distance between the heat sinks
13, 14 is in the range between 1 and 2 mm.
[0022] As shown by a bold line in FIG. 1, a coating resin 17 made
of polyamide resin is applied on the surfaces of the heat sinks 13,
14, the chip 12, and the heat sink coupler 15 to improve adhesion
between a mold resin 19 and the heat sink members 13, 14. In this
embodiment, the resin 17 is coated by immersion. Two insulating
sheets 18, which are made of a material that deforms when
compressed and is highly heat conductive, are adhered to the outer
surface of the heat sinks 13, 14. The insulating sheets 18 are
adhered using the resin 17 as adhesive, so no dedicated adhesive is
needed.
[0023] The insulating sheets 18 used in this embodiment are made of
silicon rubber and have the same thickness and the same surface
characteristics. The heat conductivity of the sheets 18 is higher
than that of the resin 19. However, the insulating sheets may
differ in material, thickness, and surface characteristics from
each other. For example, one of those insulating sheets 18 may be
made of the same material as the other but may be thinner than the
other to improve heat conduction or may have an uneven surface to
improve damping efficiency. One of the sheets 18 may be made of a
material having superior heat conductivity and inferior damping
efficiency and the other may be made of a material having inferior
heat conductivity and superior damping efficiency.
[0024] In general, the heat conducting sheets 18 are made of
elastic polymer material that includes a heat conductive filler,
and heat conductivity is improved at the expense of elasticity.
Therefore, heat conductivity takes priority if one side of the chip
is particularly hot. For example, the sheet 18 adhered to the lower
heat sink 13 may be given greater conductivity than the upper sheet
18 if the lower heat sink corresponds to a collector electrode,
which requires greater cooling.
[0025] As shown in FIG. 1, the mold resin 19, which is made of a
material such as epoxy resin, fills the space between the
insulating sheets 13, 14 to surround the chip 12 and the heat sink
coupler 15. A mold 20 is used to mold the resin 19 to a stack that
includes the semiconductor chip 12, the heat sink coupler 15, the
heat sinks 13, 14, and the insulating sheets 18. The mold 20 has a
simple structure of a lower mold 21 and an upper mold 22, so the
production cost of the semiconductor device 11 is relatively low.
When the stack is held in a cavity 23 of the mold 20, the
insulating sheets 18 are pressed between the mold 20 and the heat
sinks 13, 14 and compressively deformed by about 10 to 40%.
Therefore, when the molten mold resin 19 is injected into the
cavity 23, the resin 19 is prevented from covering the insulating
sheets 18 on the surface pressed by the mold 20. In addition, the
force applied to the chip 12 while the stack is pressed by the mold
20 is dampened and distributed by the sheets 18, so the chip 12 is
not broken.
[0026] The outward surfaces of the heat sinks 13, 14 are insulated
by the sheets 18. Thus, no dedicated heat conducting sheets made of
insulating material (like the sheets 10 in FIG. 5) are needed when
the completed device 11 is inspected, screened, assembled into a
unit such as an inverter unit, or located between cooling plates
28, 29 as shown in FIG. 3.
[0027] The thickness of the semiconductor device 11, that is, the
distance between the outer surfaces of the lower and the upper heat
sinks 13 and 14, is nominally determined by the manufacturing
method described later. However, the thickness varies due to
deviation in various factors such as the size of each member and
the flatness and inclination of the heat sinks 13, 14. Assuming
that the deviation is 0.1 mm and the sheets 18 are compressively
deformable by 15%, the minimum thickness of the sheets 18 is
calculated by the following equation.
0.1 mm.div.0.15.div.2=0.33 mm
[0028] Thus, the sheets 18 must have a thickness of at least 0.33
mm. The minimum thickness must to be adjusted in response to the
thickness deviation of the semiconductor device 11 on a
case-by-case basis.
[0029] The semiconductor device 11 is manufactured as shown in
FIGS. 2A to 2E. First, the semiconductor chip 12, the heat sink
coupler 15, and the lower heat sink 13 are soldered together. To be
specific, the chip 12, the coupler 15, and a pair of solder foils
24 are stacked on the upper surface of the lower heat sink 13, as
shown in FIGS. 2A and 2B. Then, the stack is heated by a
solder-reflowing apparatus to fuse the solder foils 24. As shown in
FIG. 2C, a pair of control electrodes of the chip 12, which may
include a gate pad, are wire bonded to lead frames 25a and 25b
using wires 26 made of metal such as aluminum or gold. Afterward,
the upper heat sink 14 and the solder foil 24 are stacked on the
coupler 15, as shown in FIG. 2D. The stack is heated by a
solder-reflowing apparatus to fuse the solder foil 24. While the
stack is heated, the stack is pressed by a weight 27, and a spacer
(not illustrated) is located between the heat sinks 13, 14 to
retain a predetermined distance between the heat sinks 13, 14, as
shown in FIG. 2E.
[0030] Before the solder foils 24 are fused, the distance between
the heat sinks 13 and 14 is greater than the predetermined
distance. When the solder foils 24 are fused, the fused solder
foils 24 become thinner, because the foils 24 are pressed by the
weight 27, and the predetermined distance is retained by the spacer
between the heat sinks 13 and 14. The fused foils 24 mechanically
and electrically connect the heat sink 13 and the chip 12, the chip
12 and the coupler 15, and the coupler 15 and the heat sink 14. In
this embodiment, the solder foils 24 are used. However, instead of
the foils 24, solder paste or conductive adhesive may also be
used.
[0031] Subsequently, the coating resin 17, which is made of
polyamide resin, is homogeneously coated on the surfaces of the
heat sinks 13, 14, the chip 12, and the heat sink coupler 15 by
immersing the soldered stack in polyamide resin solution. In this
immersion, the coating resin 17 is also applied to the surfaces of
the wires 26 and the lead frames 25a, 25b. Instead of the
immersion, the coating may be done by dripping or spraying the
resin 17. In that case, it is preferred to insert a nozzle
dispensing the resin 17 into the space between the heat sinks 13,
14 and drip or spray the resin 17 from the tip of the nozzle.
[0032] In this embodiment, the insulating sheets 18 are adhered to
the heat sinks 13, 14 before the resin 17 dries, so no dedicated
adhesive is needed. That is, the resin 17 doubles as adhesive.
However, the sheet 18 may be adhered using an adhesive that has
good heat conductivity after the resin 17 is thoroughly dried.
[0033] As shown in FIG. 1, the stack, which is coated with the
resin 17, is put in the cavity 23 of the mold 20, which has the
lower mold 21 and the upper mold 22, and is partially covered with
the mold resin 19. The molten mold resin 19 is injected into the
cavity 23 fill the space between the insulating sheets 18 and to
surround chip 12, the heat sink coupler 15, and the heat sinks 13,
14, shown in FIG. 1. After the resin 19 is set, the completed
device is ejected from the mold 20.
* * * * *